Apparatus and method for automatically compensating for lateral runout

ABSTRACT

An on-car disc brake lathe system for resurfacing a brake disc of a vehicle brake assembly includes a lathe body with a driving motor, a cutting head operably attached to the lathe body, and a drive shaft. The system also includes an alignment system having an electronic controller, input and output adaptors configured to rotate with the drive shaft, one or more adjustment discs, and an adjustment mechanism. The adjustment disc is positioned between the input adaptor and the output adaptor, and an axial alignment of the input adaptor relative to the output adaptor may be varied based on a rotational orientation of the adjustment disc. The adjustment mechanism is configured to change the rotational orientation of the adjustment disc in response to commands from the electronic controller.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 09/562,917, filedMay 2, 2000, which is a continuation of U.S. Ser. No. 09/182,429, filedOct. 30, 1998 (now U.S. Pat. No. 6,101,911), which is acontinuation-in-part of U.S. Ser. No. 08/706,512, filed Sep. 4, 1996(now U.S. Pat. No. 5,974,878) and a continuation-in-part of U.S. Ser.No. 08/706,514, filed Sep. 4, 1996 now U.S. Pat. No. 6,050,160. Theseapplications are incorporated by reference.

TECHNICAL FIELD

The invention relates to on-car brake lathes.

BACKGROUND

A brake system is one of the primary safety features in every roadvehicle. The ability to quickly decelerate and bring a vehicle to acontrolled stop is critical to the safety of the vehicle occupants andthose in the immediate vicinity. For this reason, a vehicle brakingsystem is designed and manufactured to exacting specifications and issubject to rigorous inspection.

Disc brake assemblies, which are typically mounted on the front wheelsof most passenger vehicles, are primary components of a brake system.Generally, a disc brake assembly includes a caliper that cooperates witha brake hydraulic system, a pair of brake pads, a hub, and a rotor. Thecaliper supports and positions the pair of brake pads on opposing sidesof the brake rotor. In a hubless brake rotor (i.e. when the rotor andhub are separate components), the rotor is secured to the vehicle hubwith a series of bolts and a rotor hat. The rotor rotates with the hubabout a vehicle spindle axis. When a vehicle driver depresses a brakepedal to activate the hydraulic system, the brake pads are forcedtogether and toward the rotor to grip friction surfaces of the rotor.

Disc brake assemblies must be maintained to the manufacturer'sspecifications throughout the life of the vehicle to assure optimumperformance and maximum safety. However, several problems have plaguedthe automotive industry since the inception of disc brakes.

A significant problem in brake systems is usually referred to as“lateral runout.” Generally, lateral runout is the side-to-side movementof the friction surfaces of the rotor as the rotor rotates with thevehicle hub about a spindle axis. Referring to FIG. 1, for example, arotor having friction surfaces on its lateral sides is mounted on avehicle hub for rotation about the horizontal spindle axis X. In anoptimum rotor configuration, the rotor is mounted to rotate in a plane Ythat is precisely perpendicular to the spindle axis X. Generally, goodbraking performance is dependant upon the rotor friction surfaces beingperpendicular to the spindle's axis of rotation X and being parallel toone another. In the optimum configuration, the opposing brake padscontact the friction surfaces of the rotor at perfect 90 degree anglesand exert equal pressure on the rotor as it rotates. More typically,however, the disc brake assembly produces at least a degree of lateralrunout that deviates from the ideal configuration. For example, a rotoroften will rotate in a canted plane Y′ and about an axis X′ that is afew thousandths of an inch out of axial alignment with the spindle(shown in exaggerated fashion in FIG. 1). In this rotor configuration,the brake pads, which are perpendicular to the spindle axis X, do notcontact the friction surfaces of the rotor along a constant pressureplane.

The lateral runout of a rotor is the lateral distance that the rotordeviates from the ideal plane of rotation Y during a rotation cycle. Acertain amount of lateral runout is inherently present in the hub androtor assembly. This lateral runout often results from defects inindividual components. For example, rotor friction surface runoutresults when the rotor friction surfaces are not perpendicular to therotor's own axis of rotation, rotor hat runout results when the hatconnection includes deviations that produce an off center mount, andstacked runout results when the runouts of the components are added or“stacked” with each other. An excessive amount of lateral runout in acomponent or in the assembly (i.e., stacked runout) will generallyresult in brake noise, pedal pulsation, and a significant reduction inoverall brake system efficiency. Moreover, brake pad wear is uneven andaccelerated with the presence of lateral runout. Typically,manufacturers specify a maximum lateral runout for the frictionsurfaces, rotor hat, and hub that is acceptable for safe and reliableoperation.

After extended use, a brake rotor must be resurfaced to bring the brakeassembly within manufacturers' specifications. This resurfacing istypically accomplished through a grinding or cutting operation. Severalprior art brake lathes have been used to resurface brake rotors. Theseprior art lathes can be categorized into three general classes: (1)bench-mounted lathes; (2) on-car caliper-mounted lathes; and (3) on-carhub-mounted lathes.

In general, bench-mounted lathes are inefficient and do not have rotormatching capabilities. To resurface a rotor on a bench-mounted lathe,the operator is first required to completely remove the rotor from thehub assembly. The operator then mounts the rotor on the bench latheusing a series of cones or adaptors. After the cutting operation, theoperator remounts the rotor on the vehicle spindle. Even if the rotor ismounted on the lathe in a perfectly centered and runout-free manner, thebench lathe resurfacing operation does not account for runout betweenthe rotor and hub. In addition, bench lathes are susceptible to bentshafts which introduce runout into a machined rotor. This runout is thencarried back to the brake assembly where it may combine with hub runoutto produced a stacked runout effect.

Similarly, caliper-mounted lathes have had limited success incompensating for lateral runout, and require time consuming manualoperations. During a rotor resurfacing procedure, the brake caliper mustbe removed to expose the rotor and hub. Once this is done, the calipermounting bracket is used to mount the on-car caliper-mounted lathe.Caliper-mounted lathes lack a “rigid loop” connection between thedriving motor and cutting tools, and are unable to assure aperpendicular relationship between the cutting tools and the rotor. Nordoes a typical caliper-mounted lathe have a reliable means for measuringand correcting lateral runout. Typically, such lathes use a dialindicator to determine the total amount of lateral runout in the discassembly. This measurement technique is problematic in terms of time,accuracy, and ease of use.

On-car hub-mounted lathes, generally are the most accurate and efficientmeans for resurfacing the rotor. Such a lathe is disclosed in U.S. Pat.No. 4,226,146, which is incorporated by reference.

Referring now to FIG. 2, an on-car disc brake lathe 10 may be mounted tothe hub of a vehicle 14. The lathe 10 includes a body 16, a drivingmotor 18, an adaptor 20, and a cutting assembly 22 including cuttingtools 23. The lathe may be used with a stand or an anti-rotation post(not shown), either of which can counter the rotation of the latheduring a resurfacing operation. After the brake caliper is removed, theadaptor 20 is secured to the hub of the vehicle 14 using the wheel lugnuts. The lathe body 16 is then mounted to the adaptor 20, theorientation of which may be adjusted using adjustment screws 24.

The operator then determines the total amount of lateral runout andmakes an appropriate adjustment. Specifically, the operator mounts adial indicator 26 to the cutting head 22 using a knob 28. The dialindicator 26 is positioned to contact the vehicle 14 at one of itsdistal ends as shown in FIG. 2. Once the dial indicator 26 is properlypositioned, the operator takes the following steps to measure andcompensate for lateral runout:

(1) The operator mates the lathe to the rotor using the adaptor.

(2) The operator activates the lathe motor 18, which rotates the adaptor20, the brake assembly hub, and the rotor. The total lateral runout ofthe assembly is reflected by corresponding lateral movement in the lathebody.

(3) The lateral movement of the lathe body is then quantified using thedial indicator 26. Specifically, the operator observes the dialindicator to determine the high and low deflection points and thecorresponding location of these points on the lathe.

(4) Upon identifying the highest deflection of the dial indicator, theoperator stops the rotation at the point of the identified highestdeflection.

(5) The operator then adjusts the lathe to compensate for runout of theassembly. This is accomplished by careful turning of the adjustmentscrews 24. There are four adjustment screws. The screw or screws to beturned depend on the location of the high deflection point. Turning thescrews adjusts the orientation of the lathe body with respect to theadaptor 20 (and therefore with respect to the rotor and hub) tomechanically compensate for the runout of the assembly. The operatoradjusts the screws until the highest deflection point is reduced by halfas determined by reference to the dial indicator 26.

(6) The operator activates the lathe motor 18 and observes the dialindicator 26 to again identify the highest deflection of the dial. Ifthe maximum lateral movement of the lathe body, as measured by theneedle deflection, is acceptable (i.e. typically less than {fraction(3/1000)} of an inch) then mechanical compensation is complete and thelathe resurfacing operation can commence. Otherwise, further measurementand adjustment is made by repeating steps (1) to (6). The resurfacingoperation is then performed by adjusting the tool holder 22 and cuttingtools 23 to set the proper cutting depth.

Although the hub mounted on-car brake lathe was a considerable advanceover prior brake lathes, its structure and the corresponding procedurefor compensating for lateral runout of the disc brake assembly haspractical limitations. First, the procedure requires a significantamount of time to determine and adjust for lateral runout of the brakeassembly. Although the specific amount of time necessary will vary basedupon operator experience, the time for even the most experiencedoperator is significant and can substantially increase the costassociated with rotor resurfacing. Second, the procedure requiresextensive education and operator training to assure that propermechanical compensation for lateral runout is accomplished. Moreover,the accuracy and success of measurement and adjustment of lateral runoutwill vary from operator to operator.

SUMMARY

In one general aspect, an on-car disc brake lathe system for resurfacinga brake disc of a vehicle brake assembly includes a lathe body with adriving motor, a cutting head operably attached to the lathe body, and adrive shaft. The system further includes an alignment system includingan electronic controller, an input adaptor configured to rotate with thedrive shaft, an output adaptor configured to rotate with the driveshaft, and at least one adjustment disc positioned between the inputadaptor and the output adaptor. Axial alignment of the input adaptorrelative to the output adaptor may be varied based on a rotationalorientation of the adjustment disc. An adjustment mechanism changes therotational orientation of the adjustment disc in response to commandsfrom the electronic controller.

Embodiments may include one or more of the following features. Forexample, the adjustment mechanism may include a stop disc operable in afirst state to follow the rotation of the drive shaft and operable in asecond state to rotate relative to the rotation of the drive shaft tochange the rotational orientation of the adjustment disc. The adjustmentmechanism may include a stop mechanism associated with the stop disc andoperable to move between a first position in which the stop discoperates in the first state and a second position in which the stop discis caused to operate in the second state. The stop disc may include apair of stop discs, with the first stop disc operating in the firststate when the stop mechanism is in the first position, in the secondstate when the stop mechanism is in the second position at a first time,and in the first state when the stop mechanism is in the second positionat a second time different from the first time. The second stop discoperates in the first state when the stop mechanism is in the firstposition and when the stop mechanism is in the second position at thefirst time, and operates in the second state when the stop mechanism isin the second position at the second time.

The system may include a second adjustment disc positioned between theinput adaptor and the output adaptor. The axial alignment of the inputadaptor relative to the output adaptor may be varied based on therotational orientation of the adjustment discs relative to each other. Astop disc or a pair of stop discs may be associated with each adjustmentdisc. A single stop mechanism may be associated with all of the stopdiscs. Gear trains may be associated with the stop discs, and may beconfigured to follow the movement of the respective stop discs, and tocause movement of the adjustment discs.

The adjustment discs may be slant discs that each include a slantedsurface. The adjustment discs may be arranged so that the slantedsurfaces are opposed to each other in an abutting relationship.

The stop discs may be starwheels having protruding teeth. The stopmechanism may be operable to move between a first position in which thestop disc operates in the first state and a second position in which thestop disc is caused to operate in the second state. For example, thestop mechanism may include an electromagnetic element and a toothedcatch member operable to engage at least one tooth of the starwheel. Thecontroller may be configured to time actuation of the electromagneticelement such that the toothed catch moves into its first stop positionto contact a specified tooth of the starwheel.

The system also may include a component for measuring lateral runout ofa brake disc and providing the measurement to the electronic controller.The electronic controller may issue commands to the adjustment mechanismbased on the measurement.

The systems and techniques provide automatic compensation for thelateral runout of a lathe apparatus with respect to a vehicle hub. Tothis end, the brake lathe system includes a runout measurement andcontrol system that determines the runout of a disc brake assembly anddirects a corrective signal to an automated control system to compensatefor lateral runout. The techniques may also be used in other practicalapplications to align two concentrically attached rotating shafts.

To provide automatic compensation for lateral runout, a brake latheincludes an automatic alignment coupling that operates in response to acorrective signal to adjust the alignment of the lathe with respect tothe vehicle to mechanically compensate for lateral runout. The automaticalignment mechanism may include one or more stop discs that rotate withthe drive shaft of the lathe and that can be selectively stopped fromrotating with the shaft by a stop mechanism. In response to suchstopping, one or more adjustment discs are caused to rotate to adjustthe relative position of the axis of the lathe with respect to the axisof the disc brake assembly. In this manner, the system compensates forand corrects lateral runout that exists between two concentricallyattached rotating shafts. Other techniques may also be used tocompensate for the lateral runout.

Other features and advantages will be apparent from the followingdescription, including the drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graphical representation of a lateral runout phenomenon.

FIG. 2 is a plan view showing an on-car disc brake lathe and depicting aprior art procedure for measuring, and compensating for lateral runoutof a disc brake assembly.

FIG. 3 is a perspective view showing an on-car disc brake lathe mountedon the hub of a vehicle in preparation for a disc resurfacing operation.

FIG. 4 is a partially sectional schematic view of a disc brake lathewith an automatic alignment apparatus.

FIGS. 5A and 5B are cross-sectional and front views, respectively, ofthe automatic alignment apparatus of FIG. 4.

FIG. 6 is a cross-sectional view of the adjustment disc assemblies ofthe automatic alignment apparatus of FIG. 4.

FIGS. 7A and 7B are front cross-sectional views of one of the adjustmentdisc assemblies of the automatic alignment apparatus of FIG. 4.

FIGS. 8 and 9 are cross-sectional views of the adjustment discassemblies of the automatic alignment apparatus of FIG. 4.

FIGS. 10A and 10B are cross-sectional and side views, respectively, ofan automatic alignment apparatus.

FIGS. 10C and 10C-1 are front and cross-sectional views, respectively,of an adjustment disc of the automatic alignment apparatus of FIGS. 10Aand 10B.

FIGS. 10D and 10D-1 are front and cross-sectional views, respectively,of a slant disc of the automatic alignment apparatus of FIGS. 10A and10B.

FIGS. 11A and 11B are schematic representations of the compensationvector and compensation alignment angle of the automatic alignmentapparatus of FIGS. 10A and 10B.

FIG. 12 is a cross-sectional view of an automatic alignment apparatus.

FIGS. 13A and 13B are front views of input and output adaptor assembliesand a front view of the drive arm assembly, respectively, of theautomatic alignment apparatus of FIG. 12.

FIG. 14 is a front view of a starwheel stop mechanism of the automaticalignment apparatus of FIG. 12.

FIG. 15A is a timing diagram of the hall transducer timing pulse duringthe starwheel stop operation of the automatic alignment apparatus ofFIG. 12.

FIG. 15B is a timing diagram of the forward starwheel position duringthe starwheel stop operation of the automatic alignment apparatus ofFIG. 12.

FIG. 15C is a timing diagram of the forward starwheel single stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

FIG. 15D is a timing diagram of the forward starwheel dual stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

FIG. 15E is a timing diagram of the reverse starwheel position duringthe starwheel stop operation of the automatic alignment apparatus ofFIG. 12.

FIG. 15F is a timing diagram of the reverse starwheel single stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

FIG. 15G is a timing diagram of the reverse starwheel dual stopactuation during the starwheel stop operation of the automatic alignmentapparatus of FIG. 12.

FIG. 16 is a flow diagram of an automatic alignment operation using theautomatic alignment apparatus of FIG. 12.

FIG. 17 is a schematic view of the rotational runout phenomenonoccurring during a cutting operation of the on-car disc brake lathemounted on the hub of a vehicle.

FIG. 18 is a schematic view of the linear runout phenomenon occurringduring a cutting operation of the on-car disc brake lathe mounted on thehub of a vehicle.

FIGS. 19A and 19B are front and cross-sectional views, respectively, ofa rotary piezo-electric accelerometer.

FIG. 20 is a front view of a rotary tuned coil oscillator accelerometer.

FIG. 21 is a front view of a rotary magnetic hall effect transducer.

FIGS. 22 and 22A are front and side views of a rotary infrared generatoraccelerometer.

FIGS. 23 and 23A are front and side views of a rotary accelerometeremploying a magnetic spring.

FIGS. 24 and 24A are side and top views of a rotary accelerometeremploying a magnetic spring and electrical heating.

FIG. 25 is a circuit diagram of a control system of a runout measurementand control system.

FIGS. 26 and 28 are section side views of a runout adjustment mechanism.

FIGS. 27 and 29 are end views of the mechanism of FIG. 26.

FIGS. 30 and 31 are timing diagrams associated with the mechanism ofFIG. 26.

FIGS. 32 and 33 are side and end views of a ball-and-socket jointadaptor.

FIGS. 34 and 35 are side and end views of an adaptor usingservo-controlled extenders.

DETAILED DESCRIPTION

Referring to FIG. 3, an on-car disc brake lathe 30 is mounted to a hub31 of a brake assembly of a vehicle 14. The brake lathe 30 includes amotor 32, a body 34, a cutting head 36 with cutting tools 38, and anadaptor 40. The vehicle disc brake assembly includes a rotor 42 operablyattached to the hub 31. Typically, the attachment of the rotor 42 to thehub is through a rotor hat (not shown) formed in the rotor 42 (i.e., therotor is a “hubless” rotor). However, an integral rotor and hub mayoccasionally be used in commercial vehicles. The adaptor 40 is mountedto the hub 31 of the vehicle using the lug nuts 46 normally used tosecure the hub 31 to a wheel.

FIGS. 4-9 illustrate a on-car disc brake lathe with an automaticalignment and compensation mechanism. Referring to FIG. 4, a lathe 48includes an automatic alignment mechanism 50, a lathe housing or body52, a hub adaptor 54, and a drawbar assembly 56. The hub adaptor 54corresponds to the adaptor 40 of the lathe 30, and is used to connectthe lathe 48 to the hub 31 of a vehicle 14. The drawbar assemblyincludes a drawbar 58 that extends through the body 52 and alignmentmechanism 50. The drawbar 58 is operably connected to the adaptor 54 bya threaded connection (as shown) or the like. A calibration knob 60 istightened during the automated alignment sequence of the lathe. Afteralignment is complete, a run knob 62 is tightened for the cuttingoperation. Spring 64 is a belleville washer that provides a loadingforce on bar 58 and the other components of the lathe.

Referring to FIGS. 5A and 5B, the automatic alignment coupling 50includes an input adaptor 66 operably attached to a rotating drive shaftof the lathe machine (shown in phantom in FIG. 4). A shaft 68 isattached to the input adaptor 66 such that the mounting face of theadaptor 66 is perpendicular to the shaft 68 axis so that shaft 68 runstrue with the axis of the lathe machine.

Two slant or adjustment disc assemblies 70 and 72 are interposed betweenthe input adaptor 66 and an alignment drive disc 74 which is attached tothe shaft 68 and caused to rotate with the shaft by a key 76 and a setscrew 78. A pivot plate 80 is operably attached to an output adaptor 82and mounted to the shaft 68 by a spherical bearing 84 to permit thepivot plate 80 to pivot in relation to shaft 68 while being constrainedfrom radial movement.

A pin 86, inserted into pivot plate 80, fits into a slot 88 at theperiphery of the drive disc 74 and rotationally couples the pivot plate80 to the shaft 68 and the input adaptor 66. As such, when the inputadaptor 66 is mounted on the lathe machine's drive shaft and the outputadaptor 82 is mounted on the automobile brake disc adaptor 54, the lathemachine output rotation causes the automobile brake disc adaptor 54 torotate, which causes the brake disc to rotate.

The slant or adjustment disc assemblies 70 and 72, which are mirrors ofeach other, are placed between the input adaptor 66 and the outputadaptor 82 as shown. The axial force produced by the axially mounteddrawbar 58 causes the output adaptor 82 to be forced against slant discassembly 72 and to assume an angle to the shaft 68 that depends upon therelative rotational positions of the slant discs 90 and 92, which arecontrolled using stop discs 94 and 96.

Control of the relative rotational positions of the slant discs 90 and92 is accomplished while the lathe machine output shaft is driving theautomobile brake disc hub. Specifically, by stopping the rotation ofstop disc 94 or 96, its associated slant disc is caused to rotate inrelation to the other slant disc, thus producing a change in angle ofthe output of the adjustment disc assemblies 70 and 72 and acorresponding change in the angle of the output adaptor 82. This causesa change in the angular alignment of the lathe machine axis and theautomobile brake disc axis.

The stop discs 94 and 96 are selectively stopped by powering respectiveelectromagnetic catches 98 and 100. The catches are controlled by amicroprocessor system that operates in conjunction with a runoutmeasurement and control mechanism described in more detail below. Thelathe machine output shaft rotates at a speed that is too fast (forexample, 123.14 RPM) to allow stop and release of a stop disc andassociated slant disc for adjustment. As such, the rotation speed of theadjustment components is slowed using a gear train contained in each ofthe slant disc assemblies. The gear train extends the time permitted foradjustments in a given ½ revolution of the shaft 68 (i.e. the time ittakes to stop the relative rotation of the slant discs in ½ revolutionfor maximum angular runout adjustment). For example, the time at a shaftrotation rate of 123.14 RPM extends from 0.243 seconds for ½ revolutionof the shaft 68 to 3.297 seconds to permit easy and complete adjustmentof the slant disc assemblies 70 and 72.

Referring to FIGS. 6 and 7A, the gearing mechanism includes a gear 102containing 88 teeth. Gear 102 is coupled to rotate with shaft 68 by akey 104. A gear 106 contains 38 teeth and is mounted on a pivot 108formed on stop disc 94. Thus, when stop disc 94 is stopped by theelectromagnetic catch 98, gear 106 rotates at a much faster rate thanshaft 68. For example, if shaft 68 rotates at 123.14 RPM, gear 106rotates at 285.166 RPM. A gear 10, also mounted on pivot 108, isprovided with 36 teeth and is pinned to rotate with gear 106. Gear 110is coupled to a gear 112 that is provided with, for example, 90 teeth.As such, gear 112 rotates at 114.06 RPM, or 92.6 percent of therotational speed of shaft 68, and rotates backwards in relation to shaft68 and slant disc 92. Because slant disc 90 is pinned to gear 112, italso moves backwards in relation to shaft 68. The gear arrangement andstop discs permit the adjustment of the slant disc assemblies, andtherefore, the alignment of the lathe drive axis and the hub axis,without the need for a separate motor or power source. It is to beunderstood that the identified gear ratios and rotation speeds arepractical examples and are not intended to limit the scope of theinvention. When the stop disc 94 is released, the stop disc 94 and slantdisc 90 again rotate at the rate of the shaft 68.

A stop pin 114 secured to slant disc 92 stops the relative rotation ofthe slant discs at ½ revolution, with stop disc 94 being parallel withstop disc 96 at one extreme and being positioned to provide maximumangular runout at the other extreme. By stopping the rotation of bothstop discs 94 and 96, adjustment disc 90 and 92 remain fixed in relationto each other. Stopping the rotation of stop disc 94 alone until stoppin 114 couples to slant disc 90 causes stop disc 96, and thus outputadaptor 82, to assume the maximum angular runout position.

Referring to FIG. 8, the adjustment disc assemblies 70 and 72 andassociated adjustment discs 90 and 92 are rotated in relation to eachother so that the “slant” or wedge on respective interfaces complementeach other and the input surface of the assembly is parallel with theoutput surface. This is accomplished by stopping the stop disc 94 untilthe pin 114 couples with the slant disc 90. Thus the output adaptor 82“runs true” to the input rotation axis. The angle of the interface ofthe two slant discs has been exaggerated in the figures for clarity. Theangle is of a dimension that depends on the application of the lathe,but may be on the order of 0.323 degrees. It is noted that because theinput adaptor 66 is solidly mounted to the shaft 68 and its face isperpendicular to the axis of rotation, the adaptor 66 serves as apositioning reference to the slant disc assembly 70. Referring to FIG.9, the slant disc assemblies 70 and 72 are rotated in relation to eachother by stopping the stop disc 96 until the pin 114 couples to theslant disc 90. In this position, the slant angles on the two slant discsadd to each other to cause the output surface of the assembly and theoutput adaptor 82 to display maximum angular runout with the inputrotation axis.

The runout caused by a misalignment between the vehicle's hub axis andthe axis of the lathe can be corrected without the time consuming andinaccurate manual methods of the prior art. Additional adjustment motorsare not necessary. Accurate and automated realignment is possible whenthe system is operated in conjunction with a measurement and controlsystem of the type described below.

Another implementation incorporates the fundamental features of theimplementation disclosed above, but permits adjustment with only oneslant disc. The output pivots in one selectable axis only when driven bythe slant disc. In the implementation described above, the compensationvector (explained in more detail with reference to FIGS. 11A and 11B)necessary to adjust the angle of the output adaptor 82 could potentiallyrequire adjustment of two slant discs. The fixed pivoting axis of thisimplementation eliminates this problem by requiring only one adjustment,and, potentially, reduces the time required for shaft alignment.

Referring to FIG. 10A, an automatic alignment coupling or mechanism 120occupies the same position of the mechanism 50 shown in FIG. 4. Inputadaptor 122 attaches to the rotating shaft of the lathe machine. Shaft124 is attached to the input adaptor 122 such that the adaptor 122mounting face is perpendicular to the shaft 124 so that shaft 124 runstrue with the lathe machine axis. A second shaft 126 is placed over theshaft 124. The rotated position of the second shaft 126 relative toshaft 124 is controlled by the stop disc assembly 128. The stop discassembly 128 contains a gear train and operates similarly to the stopdisc assemblies 70 and 72. However, in this case, instead of driving aslant disc when the stop disc 130 is stopped by an electromagneticcatch, the second shaft 126 is driven and moves backwards relative tothe shaft 124. Rotary movement of the shaft 126 also controls the rotaryposition of a pivot ring assembly 132 which is firmly attached to thesecond shaft 126. An output adaptor 134 is mounted on the shaft 124,held in place by a clamp ring 136, and caused to rotate with the shaft124 by a drive disc 138.

A second stop disc assembly 130, including a gear train, is mounted onthe second shaft 126 and operates similar to stop discs 94 and 96. Theoutput of the gear train drives a single slant disc 140 as shown in FIG.10C. When stop disc 130 is stopped, the slant disc 140 moves backward inrelation to shaft 124. The axial force produced by an axially mounteddrawbar 58 (FIG. 4) causes the output adaptor 134, through the pivotring 132, to assume an angle to the shaft 124 depending upon the rotatedposition of slant disc 140.

Referring to FIG. 10B, the automatic alignment mechanism may be rotated90 degrees counterclockwise about the input axis of FIG. 10A. The pivotring 132 does not rest against the stop disc assembly 130 over itsentire surface. Rather, there are two bumps diametrically placed on theface of the pivot ring 132 which rests against the stop disc assembly130. This allows the slant disc 140 to transmit its angle to the pivotring 132 but allows the pivot ring 132 to pivot on its fixed axis pins142. Thus, once set, the compensation vector for alignment does notchange when the slant disc 140 varies the output compensation angle.FIG. 10D shows the pivot ring assembly 132 in more detail. Specifically,by making one of the bumps on the pivot ring 132 a certain amount largerthan the other, the pivot ring 132 is made to be perpendicular to theshaft 124 at one extreme position of slant disc 140 and to be at themaximum compensation angle at the other extreme. A ½ degree variance,for example, is provided between the bumps as shown in FIG. 10D.Similarly, a ½ degree variance between the bumps on slant disc 140 isprovided as shown in FIG. 10C. Thus, when the slant disc 140 and thepivot ring 132 are placed against the disc 130 with the ½ degree faceangles complementing each other, a 0 degree runout between the input andoutput adaptors is achieved. On the other hand, when the discs arerotated 180 degrees relative to each other, the angles oppose each otherand the runout is 1 degree.

FIGS. 11A and 11B depict the relationship between the compensationvector, compensation angle, and pivot axis. Generally, two parametersare of importance when aligning the rotating shafts of the lathe andbrake hub. The first parameter, referred to as the compensation vector,is defined by the rotation position at which the lateral runoutdeflection of the brake lathe is the greatest. The second parameter,referred to as the compensation angle, is defined by the angle that theinput adaptor and the output adaptor must assume in relation to eachother to compensate for this lateral runout. The compensation vector andthe compensation angle can be adjusted separately as shown in FIG. 10A.

In the implementations of FIG. 4 and FIG. 12 (described below), thecompensation vector is adjusted by stopping simultaneously the inputdisc and output disc. This does not affect the relative rotationalpositions of the discs and thus does not change the input to outputangle. Rather, adjustment of the compensation vector only changes therotational position at which the disc's angle changing capability iseffective. The compensation angle is adjusted by stopping the outputdisc only, which rotates it in relation to the input disc and thuschanges the input-to-output angle.

FIGS. 12-16 show another implementation that is similar to the firstimplementation, but differs in that the slant discs are separated fromeach other and from the input and output adaptors by pin roller thrustbearings to allow free rotation of these elements under normal axialpressure. The rotational positioning of the slant discs relative to eachother and to the input and output adaptors is performed by actuatingfour starwheels which drive the slant discs through gear trains. Inaddition, forward and reverse positioning capability of the slant discsis provided, which allows a considerable decrease in time to finalalignment.

Referring to FIG. 12, an automatic alignment coupling or mechanism 144occupies the same position of the mechanism 50 shown in FIG. 4. An inputadaptor 146 attaches to and is rotationally driven by the output shaftof the brake lathe. Adaptor 146 contains two starwheels 180 and 182 thatdrive gear trains to position an input slant disc 152, which isdescribed in more detail with reference to FIG. 13A. An adaptor cover154 serves as a cover for the gearing and as a bearing surface that runsperpendicularly true to the shaft 156, which is attached to inputadaptor 146.

Thrust bearing assembly 158 is placed between input slant disc 152 andthe bearing surface of adaptor cover 154. This bearing assembly allowsfree rotation of the slant disc 152 relative to the input adaptor 146and the attached shaft 156 while automatic alignment mechanism is underaxial pressure in normal operation. Output slant disc 160 is separatedfrom slant disc 152 by a thrust bearing assembly 162 identical to thrustbearing assembly 158 to allow output slant disc 160 to freely rotateunder axial pressure. A third thrust bearing assembly 164 is placedbetween output slant disc 160 and the output adaptor cover 166, to allowfree rotation of the output slant disc 160.

Output adaptor 168 contains a starwheel and gearing assembly comparableto that of input adaptor 146. It differs in that it is free to move toan angle that varies as much as 1 degree, for example, fromperpendicular to the shaft 156 axis. Output adaptor 158 is rotationallycoupled to the shaft 156 by means of a drive arm 170 that is keyed tothe shaft 156.

FIG. 13B shows the input side of the output adaptor 168 without thestarwheel and gears. The drive arm 170 is shown in place with key 172coupling it to the shaft 156. A drive pin 174 is positioned in theoutput adaptor 168 and fits in the slot 176 of the drive arm 170 tocause the output adaptor 168 to rotate with the shaft 156 while allowingthe output adaptor 168 to tip angularly in relation to the shaft 156.

Referring to FIG. 12, a collar 178 serves as both a bearing surface forthe inside diameter of output adaptor 168 and a shoulder to preventdisassembly of the parts when the automatic alignment mechanism is notoperating under axial pressure. A wave washer 153 or the like is placedbetween input slant disc 152 and input adaptor 146 to provide somefriction so that rotation of output slant disc 160 will not causeunwanted rotation of the input slant disc 152.

Referring to FIG. 13A, input and output adaptor assemblies preferablyinclude a forward starwheel 180 that is coupled to a gear 184 having,for example, 18 teeth. Gear 184 meshes with a gear 186 having, forexample, 56 teeth. Gear 186 is coupled to gear 188 having, for example,18 teeth. Gear 188 meshes with a ring gear 190 having, for example, 140teeth. The ring gear 190 is operably attached to a respective slant disc152 or 160 as shown in FIG. 12.

Referring again to FIG. 13A, when the entire automatic alignmentmechanism rotates at 2.05 RPS, for example, in normal operation, thestarwheel 180 can be caused to rotate by catching one or more teeth asthe starwheel 180 passes by a fixed stop mechanism comprising anelectromagnetic catch or the like. Thus, a slant disc can be caused torotate in increments relative to the automatic alignment mechanism. Thereverse starwheel 182 and gear assembly operate similarly to the forwardstarwheel 180 and gear assembly except that an additional gear 192causes the slant disc to rotate in the opposite direction when thestarwheel 182 is rotated.

Referring to FIG. 14, a starwheel stop mechanism 194 includes a toothedcatch member 196 and a magnetic element such as solenoid 198 or thelike. One stop mechanism 194 may be provided to operate in conjunctionwith the input adaptor 146 and another may be provided to operate inconjunction with the output adaptor 168.

The toothed member 196 may contain one or more teeth so as to catch oneor more starwheel teeth during each rotation of the automatic alignmentmechanism. Note that the teeth of the member 196 are spaced apart so asto allow time to lift the toothed member between starwheel contact tocontrol the amount of starwheel rotation per rotation of the automaticalignment mechanism.

As the starwheels on each adaptor 146 and 168 are in line, the action ofthe starwheel catch or stop mechanisms have to be timed in synchronismwith the rotation of the automatic alignment mechanism so that only thedesired starwheel (i.e., forward starwheel 180 or reverse starwheel 182)is actuated.

FIGS. 15A-15G show exemplary timing control diagrams for the starwheelstop mechanism 194. As shown, a hall transducer or the like produces atiming pulse that is used as a time reference point.

Referring to FIG. 16, alignment may be achieved according to a procedure300. It is noted that any suitable measurement device could be used inconjunction with the alignment mechanism. Preferably, however, thesensing and measuring device described below operates in conjunctionwith the alignment mechanisms described above. It is also noted thatalthough the alignment process is shown and described in FIG. 16 withreference to the implementation of FIG. 12, the general processalgorithm is applicable to all of the described implementations.Furthermore, the alignment apparatus and process may also beadvantageously used in other practical applications to align twoconcentrically rotating shafts.

In general, the flow diagram of FIG. 16 shows a sequence of trial anderror adjustments wherein an adjustment is initially made by stopping astarwheel on one of the adaptors and measuring the change in the runoutor alignment. If the runout improves, an additional adjustment isordered in the same direction. If the alignment worsens, an adjustmentin the opposite direction is ordered. This process is repeated until thealignment is corrected to within specifications and the lathe shaft andhub axes are aligned. Two distinct periods of adjustment are employed.In a first cycle, large adjustments are made in the orientation of slantdiscs 152 and 160 to more significantly change the alignment of theshaft and hub axes to correct runout. Once alignment reaches apredetermined low level, finer adjustments are made to correct runout towithin specified tolerances.

The runout correction process begins with initialization of severalvariables (step 302). First, the stop level of stop mechanism 194 is setto three actuations of the starwheels. This provides the large movementsof slant discs 152 and 160 at the beginning of the adjustment cycle. Inaddition, several internal counts and limits are initialized includingflag Z, flag D, and a try counter. Also, the initial specification valueis set to represent an acceptable level of runout. Typically, this valueis set to be in the order of 0.001 inches. The try counter operates whenrunout drops to a “Min” value. This counter causes the value of “Spec”to increase after the system unsuccessfully tries to reach the present“Spec” runout value a programmed number of tries or cycles. Thisprevents the system from trying to forever reach a runout value that isimpossible given the circumstances.

After initializing the variables, an initial evaluation of the runout ismade and stored as R-pres (step 303), which is representative of a basevalue of the runout. The measured runout then is compared with a runoutmeasurement that conforms to specification (step 304), which, as notedabove, is typically on the order of 0.001 inches. If the runout is lessthan 0.001 inches, the runout is determined to fall within specifiedtolerances (“Spec”) and no further compensation is required. In thiscase, a “Ready to Cut” light or similar mechanism is actuated toindicate that compensation is complete (step 305) and the procedure ends(step 306).

If further compensation is required, the value of R-pres is copied intothe memory location of R-last (step 307). Next, if R-pres does notexceed a predetermined “Min” level (step 308), the stop mechanism 196 isset to stop one tooth of the starwheel 180 or 182 per revolution (step309), a try count is incremented (step 310), and the try count isevaluated to determine whether it is at a limit (step 311).

If the try count is at its limit, the runout “Spec” limit is raised(step 312) and the try count is reset to 0 (step 313). The higher “Spec”limit usually is a value that is still acceptable but less preferredthan the original “Spec” limit (e.g. 0.001 inch). For example, a higher“Spec” of 0.003 inches is acceptable.

After resetting the try count (step 313), determining that the try countis not at the limit (step 311), or determining that R-pres is not lessthan the minimum (step 308), the flag Z is tested to determine ifstarwheel actuation has run in both directions (step 314). That is,whether both output 180 (forward) and 182 (reverse) starwheels have beenactivated. If the Z flag has been toggled twice, then flag D is toggled(step 315).

After toggling flag D (step 315) or determining that the Z flag has notbeen toggled twice (step 314), the state of flag D is determined (step316). If D equals 0, then the output only starwheel is actuated tochange the compensation angle of the system (step 317). If D equals 1,both the output and input starwheels are actuated to change thecompensation vector of the system (step 318).

The system then waits for one of two revolutions of the lathe beforeproceeding (step 319) to allow transients introduced by the laststarwheel adjustment to dissipate. The number of revolutions depends onthe ability of the rotational motion sensor to track changes in therotational motion.

Next, the runout is measured again and stored as R-pres (step 320). Ifthe new runout is less than Spec (e.g., 0.001 or 0.003 inches) (step321), the adjustment process is complete and the system proceeds withsteps 305 and 306.

R-pres then is compared to R-last, the runout from the last measurement(step 322). If R-pres is not less than R-last, then flag Z is toggled tocause motion in the opposite direction (step 323). After toggling flag Z(step 323) or determining that R-pres is less than R-last (step 322),the system sets R-last equal to R-pres (step 307) and proceeds asdiscussed above.

In this manner, the system employs a trial and error approach toreducing runout. As long as the runout continues to decrease, additionalactuations of the same starwheel occur. However, if runout worsens, theopposite starwheel is actuated to begin to correct the runout. If thisforward and reverse cycle does not improve the runout, the compensationvector is adjusted by moving both of the input and output adjustmentdiscs. A microprocessor and suitable circuitry controls the operation ofthe present invention as described below.

The alignment adjustment system is a substantial improvement over priorart devices and techniques. Once the appropriate sensor and measuringsystem is properly secured, the automatic alignment system provides formechanical compensation of the total lateral runout present in the discbrake assembly. Specifically, the alignment system adjusts the alignmentof the brake lathe component with respect to a vehicle hub to compensatefor lateral runout. This, in turn, ensures that the cutting head 36 isplaced perpendicular to the rotation axis of the hub 44.

Referring to FIGS. 17 and 18, a brake lathe assembly is coupled to awheel axle through an automatic alignment mechanism of the type shownand described above. The lathe tools are shown positioned at the end ofthe brake assembly mechanism arm and arranged to move from the center ofthe brake disc toward the outside while the drive motor causes the wheeland brake disc to rotate as described above. The solid lines show themechanism position when the wheel axis and the lathe axis are inalignment. The lathe tools cut the disc surfaces smoothly under theseconditions.

However, when runout is present, as shown in FIG. 17, the lathe willrotate back and forth when in use. The dotted lines show the wobbling ofthe lathe mechanism when the wheel axis and the lathe axis aremisaligned (in the drawing the runout is greatly exaggerated). Wobblingof the lathe mechanism and tools will cut the brake disc lateral runoutinto the rotor, which is unacceptable. At the “X” point, the mechanismchanges its position not only linearly but also in a rotational senseperpendicular to the drive axis. That is, the angle of the mechanismchanges cyclically as the wheel rotates.

The sensing devices of the runout sensing and control mechanism areplaced at this X point to optimize measurement sensitivity. The sensingdevices may be positioned such that the internal rotor axis of a deviceincluding such an axis is perpendicular to the lathe drive axis.

Referring to FIG. 18, another misalignment mode can occur when the wheelaxis and the lathe axis are in misalignment. This is referred to asoff-center misalignment. With off-center misalignment, the motion of thelathe mechanism includes only linear components so that no angularrunout occurs and no rotational motion perpendicular to the drive axisoccurs. This runout motion does not detract significantly from thesmooth cutting of the brake disc surface and can be allowed. For thisreason, the sensing device only needs to sense the rotational componentsimpressed upon its housing, and may reject all linear motion.

A number of different sensing configurations can be used as a part ofthe runout sensing and control mechanism. For example, a rotaryaccelerometer may be employed as the runout detector, in which case twooperating modes are employed. In a first mode, the natural frequency ofresonant motion of the rotor transducer is configured (as explainedbelow) to be about 1.5 times the frequency of lathe rotation. Thisconfiguration permits the accelerometer to rapidly follow changes inrunout and, therefore, provides rapid alignment, due to damping inherentin the frequency differential. However, the runout sensitivity of thesystem is less than half that of the second mode.

In the second mode, the natural frequency of resonant motion of therotor transducer is configured to be below the frequency of latherotation. This provides increased sensitivity to runout and helps tosuppress harmonics in the runout motion which can cause alignmentuncertainty. However, this mode is slower in following changes inrunout, which may slow alignment as compared to the first mode. In anyevent, the natural frequency of resonant motion should never be placedat the frequency of lathe rotation because operating in resonance withthe lathe results in an unnatural buildup of rotor-transducer motionwhich doesn't allow the accelerometer output to immediately follow therunout magnitude and seriously slows the alignment process.

Independent of the operation mode, several considerations are relevantin implementing the accelerometer. First, the accelerometer rotor shouldbe completely balanced to insure measurement of rotational accelerationswhile rejecting linear accelerations. Second, the rotation of the rotorshould be physically limited such that rotation only occurs within thesensitive area of the transducer. Finally, the natural frequency ofresonant motion of the rotor-transducer should be configured to operatein either of the modes discussed above. In this regard, the naturalfrequency depends on several variables including the mass of the rotor,the diameter of the rotor, and characteristics of a spring element.

An accelerometer embodiment using a piezo-electric element as a sensoris well suited to operate under conditions in which the naturalfrequency of resonant motion is about 1.5 times the frequency of latherotation. Some force is required to bend the element, which tends tocause a high spring rate. Other transducer approaches, which generallyemploy non-contact devices, permit the spring rate to be controlled byspring selection. As such, these approaches are well suited to eithermode one or mode two operation.

FIGS. 19A and 19B show a rotary accelerometer sensor 400. Sensor 400includes a housing 402 that encloses a rotor 404 mounted for rotation onbearings 406 and 408. The rotor 404 is carefully balanced so that allaccelerations except rotational acceleration cause no rotation of therotor 404. Rotation of the rotor 404 is sensed by a piezo electricelement 410 mounted between the housing 402 and the rotor 404. Element410 is bent by any rotation of the rotor 404 to produce a voltageproportional to the magnitude of bending. The piezo electric element 410is mounted in a slot 412 in the rotor 404 to limit rotation of the rotor404 and thereby protect the piezo electric element 410.

The piezo electric element 410 and the rotor 404 operate as a spring andmass system having a natural frequency of resonant motion. In thissystem, the rotor 404 constitutes the mass and the piezo electricelement 410 constitutes the spring. The system operates in mode one, inthat the rotor mass and diameter, and the piezo spring constant, areadjusted to obtain a resonant frequency on the order of 1.5 times thefrequency of lathe rotation.

The rotor 404 also should be suitably damped to minimize the settlingtime. This can be achieved by filling the housing 402 with a viscousfluid and sealing the housing with a cover. Alternatively, damping canbe provided by using a clinging viscous material in the bearings 406 and408. Other damping techniques may also be employed.

The piezo electric element 410 produces a voltage having a magnitudeproportional to the magnitude of the angular runout. This control signalis supplied to a control system.

The sensing device may employ alternative transducing elements toprovide the control signal. For example, as shown in FIG. 20, thesensing device may employ an accelerometer with a tuned coil oscillator.The spring component of this system includes a wire (preferably music orpiano wire) 425 that is attached to a body 427 and rotor 429 as shown.The wire may be attached by any suitable means, such as, for example,brackets 431. As previously noted, the natural frequency of resonantmotion of the rotor-transducer depends on the mass and diameter of therotor and the spring characteristics of the wire. When using a musicwire 425 to control frequency as shown, the diameter of the wire and thetension in the wire 244 are manipulated to vary the frequency. Forexample, to achieve a natural frequency or resonant motion of therotor-transducer that is below the frequency of lathe rotation, adiameter in the range of approximately 9-10 thousandths of an inch isused and the wire tension is configured to be relatively loose. On theother hand, to achieve a natural frequency of resonant motion of therotor-transducer that is about 1.5 times the frequency of latherotation, a diameter on the order of approximately 16 thousandths of aninch is used and the wire tension is configured to be relatively tight.

A ferrite or the like disc 433 is placed in the periphery of the rotor429 adjacent to a housing-mounted coil 435 which serves as the inductorof an oscillator circuit 437. When the rotor 429 turns, the ferrite disc433 moves in relation to the coil 435, causing a change in theinductance of the coil and a corresponding change in the frequency ofoscillation. A discriminator 439 converts the change in frequency ofoscillation to a varying DC voltage. This varying voltage reflects therotation of the accelerometer housing 427. The signal is then forwardedto the control system.

As previously noted, it is important to configure the rotor such that itis balanced. To limit the rotation of the rotor such that rotation onlyoccurs within the sensitive area of the transducer, a counterbore 441 isprovided to cooperate with a pin 443 to limit rotor rotation asappropriate. Other limiting means may also be used.

Referring to FIG. 21, an accelerometer with a magnet 450 and a halleffect transducer 452 also may be used. In this configuration, a leafspring 454 has a spring rate which, in combination with the inertia ofthe rotor 456, provides a resonant frequency about 1.5 times therotational rate of the brake lathe shaft (i.e. operation in mode one).Alternatively, the accelerometer could be configured to operate in modeone or two using a music wire as described above.

The magnet 450 is placed in the periphery of the rotor 456. The halleffect transducer 452 has a linear characteristic and is placed in thehousing 458 adjacent to the magnet 450 such that rotary motion of therotor is reflected in the output voltage of the hall effect transducer452. The magnitude of the AC voltage at the output of the hall effecttransducer 452 is a reflection of the rotary motion of the accelerometerhousing 458 that is attached to the lathe, preferably at the positionidentified with reference to FIGS. 17 and 18. The resulting signal isforwarded to a control system.

In yet another implementation, as shown in FIGS. 22 and 22A, the sensingelement may includes an accelerometer with an infrared generator. A leafspring 475 has a spring constant which, in combination with the inertiaof a rotor 477, provides a resonant frequency about 1.5 times therotational rate of the brake lathe shaft. Again, this accelerometercould alternatively be configured to operate in mode one or two using amusic wire as described above. An infrared generator diode 479 is placedfacing an infrared detector diode 481 on the housing 483 near theperiphery of the rotor 477.

A shutter 485 is attached to the rotor 477 and projects between the IRgenerator 479 and IR detector 481 such that rotary motion of the rotor477 varies the amount of radiant energy transferred, causing the voltageproduced by the IR detector 481 to reflect the magnitude of rotation ofthe housing 483 (i.e., the runout of the disc coupling). The signal thenis forwarded to the control system.

Referring to FIGS. 23 and 23A, yet another implementation employs aninfrared sensor and detector as described above. The rotor 500 has amagnet 502, such as a Neo Iron Boron type magnet available fromJobmaster as Part No. NE0270200N, embedded in its upper face. Alinearly-adjustable tapped block 504 is mounted on the underside of thecover 506 of the accelerometer housing 508. A permeable screw 510threads into the block 504 and is positioned so that, with the covermounted on the housing, the end of the screw sits just above the magnet502.

The block 504 may be adjusted using screws 512 in slots 514 to positionthe rotor 500 by magnetic attraction. This permits positioning of therotor so that the shutter 516 interrupts infrared energy in an infraredsensor assembly 518 using a generator and detector as described abovewith reference FIGS. 22 and 22A to provide a desired steady state DCoutput voltage.

Turning the permeable screw 510 to move it toward the magnet 502provides an increase in magnetic attraction and consequent increases inthe spring constant and the natural frequency at which the rotor rings.Moving the screw away from the magnet 502 has the opposite effect.

With good bearings, the rotor has low loss such that rotary mode ringingoccurs for several seconds after the rotor is actuated. This is notdesirable since it impedes the accelerometers ability to follow achanging actuating force.

Ringing is reduced by damping provided by a ferro fluid 520, such as isavailable from Ferrofluidics Corporation. A ferro fluid is an oil-basedfluid with a suspension of microscopic permeable particles that causethe fluid to cling to a magnet.

The permeable screw, the ferro fluid, and the-magnet are arranged in aplastic cup 522 in the periphery of the rotor. A drop of ferro fluid 520on the magnet 502 clings to the interface between the magnet and thepermeable screw. The fluid is of sufficient viscosity to damp the rotorto reduce ringing time by a factor of three. To prevent unwantedinteraction between the fluid and the surface of the magnet, the magnetmay be covered by a piece of Teflon tape to seal the surface of themagnet.

The viscosity of the ferro fluid is temperature sensitive. This meansthat system performance may vary with varying temperature.

Referring to FIGS. 24 and 24A, temperature sensitivity may be reduced byheating the fluid. A thermally conductive block 525, which may be metal,is used for electrical heating. Block 525 is larger than the unheatedblock 504 to allow for a slot into which a positive temperaturecoefficient (PTC) resistance element 527 may be potted using thermallyconductive epoxy. The PTC element 527 is supplied by wires 529 from afixed DC voltage source.

To thermally isolate the block 525 from the cover 506, an insulating pad531 is placed between the two. The block 525 is held in place by nylonscrews 533 to further thermally isolate the block.

In yet another variation, the accelerometer is replaced by an angularrate sensor that employs a pair of micromachined tuning forks. Rotationof the sensor induces a Coriolis effect that causes a difference in theoutput of the two forks. The difference is reflected in the output ofthe sensor, and provides an indication of the rate of rotation. Such asensor is available from BEI Systron Donner Inertial Division Sensorsand Systems Company of Concord, Calif. as part number AQRS-00064-109N.

Referring to FIG. 25, the runout sensing and control mechanism furtherincludes a control circuit 600. A transducer 602 may be implementedusing an accelerometer or angular rate sensor as described above toevaluate the rotational acceleration of the lathe. Because lateralrunout manifests itself in varying rotational motion imparted to thelathe, any sensor arrangement capable of producing an accuratequalitative measure of rotational acceleration may be used. Thefollowing discussion assumes that the transducer produces an alternatingcurrent signal having a magnitude that varies with the degree ofrotational motion.

The output of transducer 602 is fed to an amplifier 604 and then to arectifier 606. Because runout produces a cyclical motion in the lathe,the signal produced by transducer 602 is sinusoidal in nature. However,other wave forms could resonate at lower runout. After amplification byamplifier 604 and rectification by full wave rectifier 606, the peakrunout signal is fed to an integrator 608 that is reset during eachlathe rotation cycle. The signal is then sent to a sample and holdcircuit 610.

A hall pickup timer 612 produces a synchronization signal. This signalcauses a switch 614 to transition to discharge a capacitor 616 to resetthe integrator 608. The synchronization signal also causes a switch 618to transition to store the output value of the integrator in the sampleand hold circuit 610 prior to discharging the capacitor.

The output of the sample and hold circuit 610 is transmitted to an A/Dconverter 620 which samples the output and produces a digitalrepresentation of the voltage level. The output of the A/D converter 620is provided to a latch 622 and a microprocessor 624. The microprocessor624 also receives the output of latch 622. Latch 622 is a conventionalsample and hold latch and is clocked just prior to the time A/Dconverter 620 presents a new sample. In this manner, both the currentsample taken by A/D converter 620 and the last sample taken by A/Dconverter 620 are available to microprocessor 624. Amplifiers 626 and628 are provided at the output of microprocessor 624 to drive the stopmechanism(s).

Taken in conjunction with the algorithm set forth in FIG. 16,microprocessor 624 is thus provided with a stream of samples of therunout of the rotor under consideration, together with a samplerepresenting the last historical value of the runout. In this manner,the microprocessor implements the trial and error approach describedabove with respect to FIG. 16.

FIGS. 26-31 illustrate another implementation of the runout adjustmentmechanism. This implementation is similar to the implementation of FIG.12 in that the rotational positioning of the slant discs relative toeach other and to the input and output adaptors is performed byactuating four starwheels, or stop discs, to drive gear trains that thendrive the slant discs. In this implementation, however, the fourstarwheels are all aligned in the same plane. With this arrangement,only one stop mechanism is needed to actuate the starwheels, with thecorrect starwheel being selected through timed actuation of the stopmechanism.

The runout adjustment mechanism may be totally enclosed, so as toprevent contamination by metal chips produced as a result of the latheoperation. A separate cover is not required. The stop mechanism may bemounted adjacent to the runout adjusting mechanism and may be providedwith its own cover to prevent contamination by lathe chips.

The single-plane implementation of FIGS. 26-31 uses a reduced number ofcomponents and, accordingly, is less expensive to manufacture than theimplementation of FIG. 12. The single-plane implementation also is“stiffer” because it does not require the partially hollow input andoutput adaptors of the implementation of FIG. 12 since gearing may bepositioned at the periphery of the mechanism.

Referring to FIGS. 26 and 27, an alignment mechanism 700 occupies thesame position as the mechanism 144 of the implementation of FIG. 12. Aninput adaptor 702 is attached to and is rotationally driven by theoutput shaft 704 of a brake lathe. Input adaptor 702 includes fourstarwheels 706-712 which drive gear trains to position two slant discs,as described in more detail with reference to FIG. 28.

A stop mechanism assembly 714 is mounted on the bearing cap 716 of thebrake lathe by means of a mounting yoke 718. The stop mechanism depictedin FIGS. 28 and 29 includes a solenoid 720 coupled by a link 722 to anactuator arm 724 attached to a starwheel stopper 726. A coil spring 728serves to open the solenoid core and retract the stopper 726 when thesolenoid 720 is not powered. A stop pad 730 serves to cushion the returnof actuator arm 724 when the solenoid 720 is de-energized. In otherimplementations, the stop mechanism 714 may employ devices other than asolenoid.

When the stop mechanism 714 is activated, the actuator arm 724 forcesthe starwheel stopper 726 against the periphery of the alignmentmechanism 700 and into the path of the four starwheels 706-712. A syncmagnet 732 carried by the rotating alignment mechanism 700 passes by ahall detector 734 once each revolution. The hall detector 734 providesan output that serves as a timing signal for electronic control of thestop mechanism 714.

Referring to FIG. 28, the alignment mechanism 700 includes an outputadaptor support 736 attached to the input adaptor 702. A pin 738projects from a peripheral surface of the output adaptor support 736 andserves to rotationally couple an output adaptor 740 to the input adaptor702 so that the output adaptor 740 rotates with the brake lathe shaft704. A collar 742 serves to hold the output adaptor 740 on the outputadaptor support 736 while allowing the output adaptor 740 to tip at upto a desired angular limit (for example +/−1 degree) from perpendicularto the rotational axis.

The periphery of the output adaptor 740 is grooved to accept a rubber“O” ring 744. A seal ring 746 attached to the input adaptor 702cooperates with the “O” ring 744 to seal the interior of the mechanismagainst contamination.

Slant discs 748 and 750 serve to vary the angle between the inputadaptor 702 mounting surface and the output adaptor 740 mountingsurface. Slant discs 748 and 750, which have gear teeth on theirrespective peripheries, are mounted between the input adaptor 702 andthe output adaptor 740. Three sets of pin roller thrust bearings 752-756separate the slant discs 748 and 750 from each other and from the inputadaptor 702 and the output adaptor 740. Under normal axial pressure, thethrust bearings 752-756 allow the slant discs 748 and 750 to rotatefreely in relation to each other and in relation to the input adaptor702 and output adaptor 740.

The mounting surface of the input adaptor 702 and the mounting surfaceof the output adaptor 740 are caused to be parallel when the equallyangled faces of the slant discs 748 and 750 are rotated to a position inwhich they complement each other. The mounting surfaces are offset fromparallel when the equally angled faces of the slant discs 748 and 750are rotated to a position in which they oppose each other.

Four starwheels 706-712 attached to gears 758-764 by shafts 766-772facilitate rotational control of the slant discs 748 and 750 in relationto each other and in relation to the input adaptor 734 and the outputadaptor 740.

FIG. 29 shows the relative locations of the starwheels 706-712 and thesync magnet 732. Also shown are the brackets 774 and 776 that clasp theshaft alignment mechanism to the brake lathe output shaft 704. Shaftsrotationally couple the starwheels 706-712 to corresponding gears758-764. Gears 758 and 760 directly engage the teeth on the periphery ofthe slant discs 748 and 750, respectively. This arrangement causes slantdiscs 748 and 750 to rotate with the rotation of the respectivestarwheels 706 and 708. Gears 762 and 764 engage reverse gears 778 and780, respectively, which engage the teeth on the periphery of slantdiscs 748 and 750, respectively. Reverse gears 778 and 780 serve toreverse the rotational direction of slant discs 748 and 750 whenstarwheels 710 and 712 are rotated.

Each starwheel serves a distinct function. Starwheel 706, which may belabelled the “A Disc Forward” starwheel, is rotationally coupled to gear758 by shaft 768. Gear 758 engages the teeth on the periphery of slantdisc 748. Thus, when one of the teeth of starwheel 706 is stopped orcaught by the stopper 726, slant disc 748 (the “A Disc”) rotates in aforward direction relative to the alignment mechanism 700.

Starwheel 708, which may be labelled the “B Disc Forward Starwheel”works in a similar fashion as starwheel 706 described above, except thatwhen starwheel 708 is engaged, slant disc 750 (the “B Disc”) rotates ina forward direction.

Starwheel 710 may be labelled the “A Disc Reverse Starwheel.” Starwheel710 is rotationally coupled to gear 762 by shaft 770. Gear 762 engagesreverse gear 778, which engages the teeth along the periphery of slantdisc 748. Thus, when one of the teeth of starwheel 710 is caught by thestopper 726, gear 778 reverses the rotational direction, and slant disc748 (the “A Disc”) rotates in a reverse direction relative to thealignment mechanism 700.

Starwheel 712, which may be labelled the “B Disc Reverse Starwheel”works in a similar fashion as starwheel 710 described above, except thatwhen starwheel 712 is engaged, slant disc 750 (the “B Disc”) rotates ina reverse direction.

FIG. 30 illustrates actuation timing for adjustment of the compensationangle using the single-plane mechanism. Adjustment of the compensationangle may be achieved through incremental rotation of either of theslant discs 748 or 750 in either forward or reverse directions. With thesingle-plane implementation, control of the actuation is achievedexclusively through timing of the single stopper 726.

The concentric circles 782-788 of FIG. 30 are calibrated in time. Timezero is defined as the time, in a given revolution, at which the syncmagnet passes the hall detector, as described with reference to FIGS. 26and 27. The concentric circles in FIG. 30 show the elapsed time inmilliseconds from time zero to the calibrated point, when the alignmentmechanism 700 is rotating normally at 2.054 revolutions per second. Thetimes indicated are approximate and may be varied to achieve a desiredadjustment operation. The solid line of each of circles 782-788indicates the stopper 726 actuation period. Each of circles 782-788represents the actuation timing for a particular change in thecompensation angle.

In the diagram of FIG. 30, the stopper 726 includes two prongs. Thestopper prongs are separated such that, at the rotation rate of thealignment mechanism 700, forty milliseconds will elapse from the time astarwheel passes the first stopper prong to the time the same starwheelpasses the second stopper prong. Thus, the stopper can be actuated intime to catch a first tooth of a selected one of the starwheels 706-712with the first stopper prong, while leaving 40 milliseconds during whichthe stopper may be retracted so that the second stopper prong does notcontact a second tooth of the selected starwheel. The stopper 726 may beconfigured with more stopper prongs as needed to facilitate the desiredstarwheel actuation.

The number of teeth of a selected starwheel caught during a revolutionof the alignment mechanism 700 can be programmed. Preferably, when thealignment runout is large, the program calls speeds adjustment bycalling for two teeth of the selected starwheel to be caught during eachrevolution. This may be referred to as dual-stop actuation. As therunout approaches zero, one tooth is caught per revolution to allowfiner adjustment. This may be referred to as single-stop actuation.

Circle 782 represents a “Forward-Angle, Single-Stop” actuation. Theactuation period is indicated by the solid portion of circle 782. Thus,to adjust the compensation angle in a forward direction, the stopper 728may be actuated for 45 milliseconds beginning 122 milliseconds aftertime zero. During this period, one tooth of starwheel 706 (the “A DiscForward Starwheel) is caught by the stopper 726. As a result, slant disc748 (the “A Disc”) rotates forward by a corresponding amount relative tothe alignment mechanism 700, as described above.

Circle 784 represents a “Forward-Angle, Dual-Stop” actuation. Duringthis actuation, two teeth of starwheel 706 are caught, and slant disc748 rotates forward by a corresponding amount relative to the alignmentmechanism. The amount of slant disc 748 rotation in this actuation islarger than that of the “Forward Angle, Single Stop” actuation becausetwo teeth of starwheel 706 are caught instead of one.

Circles 786 and 788 represent the “Reverse-Angle, Single-Stop” and“Reverse-Angle, Dual-Stop” actuation periods, respectively. The reverseactuations are similar to the forward-angle actuations except thatstarwheel 710 (the “Reverse A Disc Starwheel”) is engaged so that slantdisc 748 rotates in a reverse direction relative to the alignmentmechanism 700.

FIG. 31 shows the actuation timing for adjustment of the compensationvector using the single-plane mechanism. As in FIG. 30, the concentriccircles 790-796 in FIG. 31 are calibrated and show the elapsed time inmilliseconds from time zero to the calibrated point with the alignmentmechanism 700 rotating normally at 2.054 revolutions per second. Each ofcircles 790-796 represents the actuation timing for a particular changein the compensation vector. The times indicated are approximate and maybe varied to achieve a desired adjustment operation.

Adjustment of the compensation vector may be achieved throughincremental rotation of both slant discs 748 and 750 by equal amounts inthe same direction (either forward or reverse). The compensation vectorchanges as the slant discs 748 and 750 rotate relative to the alignmentmechanism 700. However, the compensation angle remains the same. Becauseboth slant discs 748 and 750 are rotated by the same amount in the samedirection. Depending on the amount of adjustment needed, the actuationmay be single-stop or dual-stop.

Circle 790 represents a “Forward-Vector, Single-Stop” actuation. Thisprocess involves actuating the stopper 726 for a period of approximately45 milliseconds beginning at time zero, and again for 45 millisecondsbeginning 122 milliseconds after time zero, as indicated by the solidportion of circle 790. During this process, the stopper 726 firstcatches a single tooth of starwheel 712, which causes slant disc 748 torotate forward, and then catches a single tooth of starwheel 706, whichcauses slant disc 750 to rotate forward by the same amount.

Circle 792 represents a “Forward-Vector, Dual-Stop” actuation. In thisprocess, the stopper 726 is actuated for a period of 192 millisecondsbeginning at time zero. During this period, two teeth on each ofstarwheels 712 and 706 are caught and the slant discs 748 and 750 arecaused to rotate forward by a corresponding amount. Because two teethare caught on each of starwheels 712 and 706, the slant discs 748 and750 rotate by a larger amount and the compensation vector is adjusted bya larger degree than in the “Forward-Vector, Single-Stop” actuation.

Circles 794 and 796 represent “Reverse-Vector, Single-Stop” and“Reverse-Vector, Dual-Stop” actuations, respectively. These actuationprocesses are similar to the forward-vector actuations, but differ inthat starwheels 708 and 710 are engaged instead of starwheels 706 and712, so that slant discs 748 and 750 are caused to rotate in a reversedirection relative to the alignment mechanism 700.

Without attempting to set forth all of the desirable features of theinstant on-car disc brake lathe with automatic alignment system, atleast some of the major advantages include providing an on-car discbrake lathe having an automated alignment assembly 50 that includes apair of adjustment disc assemblies that are positioned between an inputadaptor 66, 122, 146 and an output adaptor 78, 134, 168. Each of theadjustment disc assemblies includes an adjustment disc 90, 92, 140, 152,160 and associated stop disc. An electromagnetic catch 98, 100 or thelike is operably associated with each of the stop discs 94, 96 andoperates in response to a control signal issued from a control system.When the rotation of one of the stop discs is stopped, rotationalmovement of the lathe drive shaft is transferred, through appropriategearing, to a respective adjustment disc to change the relative positionof the lathe drive axis and the vehicle hub axis.

The control algorithm and alignment process may include a series oftrial and error adjustment inquiries to compensate for runout. The Hallsignal serves as a timing signal. As the lathe rotates, the runout levelis evaluated. If the runout level is within the “Spec” limit, normally0.001 inches, the alignment goes to the “Ready to Cut” state, thecorresponding light is illuminated, and the program ends. If the runoutis above the “Spec” limit, an actuation of the output forward starwheelis ordered. The runout is evaluated and if lower than the previousrunout, added actuations of the same starwheel are ordered until anactuation causes the runout to increase. At this point, if the runout isstill above the “Spec” limit, an actuation of the output reversestarwheel is ordered. If the resulting runout is lower, further suchactuations are ordered until an actuation causes the runout to increase.The previous two actions adjusts the “compensation angle.” At thispoint, if the runout is still above the “Spec” limit, a tandem actuationof both the output and the input forward starwheels is ordered. Thisaction adjusts the “compensation vector.” The runout is evaluated and iflower than the previous runout, further tandem actuations of the outputand input forward starwheels are ordered until an actuation causes therunout to increase.

At this point, if the runout is still above the “Spec”, a tandemactuation of the output and input reverse starwheels is ordered. Therunout is evaluated and if lower than the previous runout, further suchactuations are ordered. If an actuation causes a runout increase, and ifthe runout is still above the “Spec” limit, the starwheel actuationsrevert to the output starwheels only mode again as described previously.This trial and error actuation sequence continues as described aboveuntil the runout is reduced to the “Spec” limit, where the “Ready toCut” light is illuminated and the program ends.

A count is kept of the number of tries to reach the “Spec” runout level.When a preset number of tries is exceeded, the acceptance level israised to about 0.003 inches. If the runout is within this level, the“Ready to Cut” light is illuminated and the program ends. If this newhigher runout level is not reached within a preset number of tries, an“Out of Spec” light is illuminated and the program ends. The operator isdirected to check the lathe coupling to the brake disc hub, to check forbad wheel bearings, to correct the problem, and to try the alignmentcycle again.

Other embodiments are within the scope of the following claims. Forexample, referring to FIGS. 32 and 33, instead of using slant discs toadjust the orientation of the input and output adaptors, a joint 800including a ball 802 and a socket 804 may be used. An extension 806attached to the ball 802 is connected to a platform 808 attached to thesocket 804 by three arms 810. The length of the arms can be adjusted tocontrol the orientation of the extension relative to the platform.

In addition, referring to FIGS. 34 and 35, an adaptor 850 having fourservo-controlled extenders 852 may be employed. A distance to which eachextender 852 extends from a surface 854 of the adaptor 850 may becontrolled to control the orientation of the adaptor 850 to acorresponding adaptor 856.

What is claimed is:
 1. An on-vehicle disc brake lathe system forresurfacing a brake disc of a vehicle brake assembly, the brake lathesystem comprising: a lathe body with a driving motor; a cutting headoperably attached to the lathe body; a drive shaft extending from thelathe body and operably connected to the driving motor so as to berotated by the driving motor; a mechanical coupling connected to tiedrive shaft and configured to provide an adjustable connection betweenthe drive shaft and the vehicle brake assembly, the mechanical couplingincluding a first component connected to the drive shaft, a secondcomponent including structure for connection to the vehicle brakeassembly, and a mechanical adjustment element between the firstcomponent and the second component, the mechanical coupling beingconfigured to vary an axial alignment of the first component relative tothe second component by moving the mechanical adjustment element; and anelectronic control system connected to the mechanical coupling andoperable to automatically adjust the adjustable connection provided bythe mechanical coupling so as to improve alignment of the cutting headrelative to an axis of rotation of the vehicle brake assembly as thedrive shaft rotates.
 2. The on-vehicle brake lathe system of claim 1wherein the driving motor is operable to initiate rotation of the driveshaft and the electronic control system is operable to sense movement ofthe lathe body resulting from rotation of the drive shaft.
 3. Theon-vehicle brake lathe system of claim 2 wherein the electronic controlsystem is operable to reduce movement of the lathe body until movementof the lathe body falls below a predetermined threshold amount.
 4. Theon-vehicle brake lathe system of claim 1 wherein the electronic controlsystem comprises a sensor operable to produce a signal indicative ofmovement of the lathe body.
 5. The on-vehicle brake lathe system ofclaim 4 wherein the electronic control system further comprises anelectronic controller connected to receive the signal from the sensor,to generate a control signal in response to the signal from the sensor,and to provide the control signal to the mechanical coupling.
 6. Theon-vehicle brake lathe system of claim 4 wherein the mechanical couplingfurther comprises a mechanism connected to receive the control signaland to change an amount by which the mechanical adjustment elementextends between the first component and the second component in responseto the control signal.
 7. The on-vehicle brake lathe system of claim 4wherein the mechanical adjustment element comprises a servo-controlledextender.
 8. The on-vehicle brake lathe system of claim 7 wherein themechanical coupling further comprises a plurality of servo-controlledextenders, each servo-controlled extender extending between the firstcomponent and the second component.
 9. The on-vehicle brake lathe systemof claim 1 wherein the mechanical coupling further comprises a pluralityof mechanical adjustment elements, each mechanical adjustment elementextending between the first component and the second component.
 10. Theon-vehicle brake lathe system of claim 1 wherein the mechanical couplingfurther comprises a joint that allows spherical motion, wherein thejoint is positioned between the first component and the secondcomponent, and the mechanical coupling comprises adjustable-length armsextending between the first component and the second component such thatan orientation of the input adaptor relative to the output adaptor isvaried by varying lengths of the arms.